Voltage regulator



April 24, 1962 R. L. VON ESCHEN ET AL VOLTAGE REGULATOR Filed July 28,1958 l 7 L REGULA r50 OUTPUT UNREGULATED /3 T DIFFERENCE T AMPLIFIERCIRCUIT UNREGULATED NW REGULA r50 INPU r L OUTPUT IN VEN 70/?5 Roben L.Van Eschen Paul F. Schee/e fiw i Attorney United States Patent 3,031,608VOLTAGE REGULATOR Robert L. Von Eschen and Paul F. Scheele, Albuquerque,

N. Mex., assignors, by mesne assignments, to the United States ofAmerica as represented by the United States Atomic Energy CommissionFiled July 28, 1958, Ser. No. 751,581 1 Claim. (Cl. 323-22) The presentinvention relates generally to voltage regulators, and more particularlyto voltage regulator circuits having a regulating transistor connectedin series with the positive line of a power system.

Series voltage regulators of this type are popular because they draw avery small amount of current from the power supply under no-loadconditions. The other basic type of regulator uses the shunt method andhas the characteristic of drawing full-load current from the powersupply at all times.

In general, the series type voltage regulator operates by comparing theregulated voltage with a reference voltage standard, deriving a voltagewhich is representative of the difference between the two and using thisdifference voltage to control the impedance of the transistor connectedin series with the supply line. A negative feedback connection is usedso that an increase in the difierence voltage causes an increase in theimpedance of the series transistor, increasing the voltage drop acrossthe transistor and thereby causing the output voltage to drop to normal.The rise in difference voltage may be due to variations in load current,input voltage, or temperature of the series transistor.

A serious limitation in the operating temperature range of seriesvoltage regulators has been the efiect of rising temperatures on theimpedance of the series transistor, which is to decrease the internalimpedance of the series transistor, thereby allowing the output voltageto rise. The difierence voltage generated therefrom then is applied tothe base of the series transistor in an attempt to increase thetransistor impedance and regain control of the voltage. The usual methodof controlling a transistor includes holding the base electrode negativewith respect to the emitter, so that there is a base current flowing outof the transistor at all times. When rising temperatures prevail,therefore, the base electrode is driven less and less negative,increasing the internal impedance, until the base reaches the samepotential as the emitter. Further control of the transistor necessitatesdriving the base electrode more positive than the emitter, reversing thedirection of flow of base current. Circuits have been devised forperforming this action in connection with NPN transistors, which are thetype of transistors usually used in the positive line of a power system.

At the present time, germanium transistors of NPN type are availableonly for low-powered applications. Silicon transistors are available tohandle large amounts of power, but their cost is several times that ofgermanium- PNP-type transistors. Therefore, in circuit applicationswhere it is necessary that a common negative lead be carried through thevoltage regulator, it is quite desirable from an economic standpointthat PNP-type transistors can be used in the more economical seriesvoltage regulator.

It is also important that circuitry be designed which will operate inthe vicinity of 180 F. for use in modern guided missile applications. Ithas been found through experience that prior art series regulators losecontrol of the voltage at approximately 140 F.

Therefore it is a general object of this invention to provide atransistor series voltage regulator having a common negative lead andhaving an operating temperature range in excess of that of prior-artregulators. The

present invention will provide very close voltage regulation up to thevicinity of F, the upper temperature limit being set only by theallowable maximum junction temperature of the series transistor, ratherthan by the decrease of base current to zero.

Briefly, the present invention includes a novel arrangement of a Zenerdiode and a resistor in the base-emitter circuit of the seriestransistor. The Zener voltage of the diode is related to the size of theresistor such that a decrease in normal current flow through theresistor will create a reversal of the polarity of the base-emittervoltage thereby reversing the direction of flow of base current andextending the useful temperature range of the series transistor. Theexistence of the Zener diode allows a similar reversal of base currentin a transistor amplifier in the negative feedback circuit as well,where a transistor amplifier is applicable.

Other objects and advantages of the present invention will becomeapparent from reading the more detailed description to follow, inconjunction with the attached drawing, in which:

FIG. 1 shows a preferred embodiment of the invention in its most generalform; and

FIG. 2 shows a more specific form of the preferred embodiment, usingsemiconductor elements in the feedback circuit.

As shown in FIG. 1, P NP transistor 10 is connected with itsemitter-collector path in series with the positive line of a powersystem which has a common negative line. Zener diode 11 is connectedbetween the positive input terminal of the voltage regulator circuit andthe emitter of transistor 10. The Zener diode has the characteristic ofa constant voltage drop across its terminals over a wide range ofcurrents flowing through the diode in a reverse direction. Therefore,the voltage drop from the positive input terminal to the emitter oftransistor 10 will remain constant over the useful range of the diode.Resistor 12 is connected from the positive input terminal to the base oftransistor 10, and to the output of amplifier 13. The amplifier isconstructed so that it draws a relatively constant amount of currentthrough resistor 12, suflicient to create a voltage drop across theresistor in excess of the Zener voltage of diode 11. The base then isnegative with respect to the emitter. This situation prevails at thelower part of the temperature range of transistor 10.

Difference circuit 14 detects a rise in the regulated output voltagecaused by any one of the several factors previously mentioned, andapplies a difference voltage to amplifier 13. The amplified difi'erencevoltage, when applied to the base of transistor 10, raises the voltagethereof, lowers the base current, and increases the impedance of thetransistor. The voltage drop across the transistor increases, with theresult that the regulated output voltage decreases to the desired value.An original decrease in regulated output voltage will have the oppositeettect on the circuit.

'If the change in output voltage is sufiicient, amplifier 13 raises thebase voltage until it equals the emitter voltage. In prior-artcircuitry, this would indicate the limit of regulation of the circuit,but in the present invention, further increase in difierence voltagedecreases the Voltage drop across resistor 12, so that it is less thanthe Zener voltage of diode 11, thereby reversing the polarity of theemitter-base bias voltage and making the base positive with respect tothe emitter. Control of the impedance of the transistor 10 is therebymaintained beyond the limit of control found in earlier circuits.

The circuit of FIG. 2 makes exclusive use of transistors and Zenerdiodes in the amplifier and in the difference circuit. The emitter-basepath of transistor 15 is connected in series with Zener diodes 16 and 17across the output terminals of the regulator. Since the voltage dropacross each of the diodes is constant, regardless of changes in theregulated output voltage, the entire change in output voltage (ordifference between the output voltage and the sum of the Zener voltages)appears between the base and the emitter of transistor 15. Thisdifference voltage is amplified and applied to the base of amplifyingtransistor 18. The further amplified signal is conducted to the base oftransistor where it performs the corrective action on the transistorimpedance. Resistor 19 limits the current through diode 16 to within itsoperating range and provides a current path for transistor 15. Resistor20 per-forms the same limiting function for diode 17, and is connectedto the positive input terminal so that an initial reference voltage willbe developed across diode 17 for proper initial operation of thecircuit. Resistor 21 furnishes collector and base currents fortransistors and 18 respectively, from the positive input terminal.

Reversal of the base currents of transistors 15 and 18 may occur asfollows: Circuit values are chosen so that at the lower part of thetemperature range of transistor 15 its base is held positive withrespect to its emitter. Diode 17 holds the base voltage constant withrespect to ground. (Since transistor 15 is a N PN-ty-pe transistor, thisis the usual polarity of the bias.) A large rise in difference voltage,however, will raise the emitter voltage above that of the base, thusreversing the bias. The emitter of transistor 18 remains at a fairlyconstant voltage, there being only changes of a few tenth-s of a voltnecessary to control the impedance of transistor 10. However, changes inthe collector current of transistor 15 are fairly large due to thechanges in difference voltage and are reflected in large changes in thevoltage drop across resistor 21. The large size of resistor 21 relativeto resistor 12 emphasizes this effect. The result is that at largeincrease in difierence voltage raises the base voltage of transistor 18,reversing the normal negative emitter-base-bias on that PNP-transistorand thereby extending its effective range.

Even if changes in input voltage and load current are not sutficient tochange the difierence voltage, the changes in internal impedances of thethree transistors due to changes in temperature frequency are enough torequire the reversal of base currents therein.

The following table lists suggested circuit values and component typesfor a preferred embodiment of the invention designed to produce a12-volt regulated output from an unregulated input voltage which mayvary between the limits of 24 volts and 33 volts. Regulation has beenfound to be within 1% over a temperature range from F. to 180 F.

Circuit element: Value or type Transistor 1t 2N1S8 Diode 11 SV906Resistor 12 ohms- 750 Transistor 15 2N228 Diodes 16, 17 1N429 Transistor1'8 2N45 Resistor 19 ohrns Resistor 20 do 3000 Resistor 21 ..do 3600 Apreferred embodiment of a novel series transistor voltage regulatorcircuit has been described as an example only. It is recognized that theuse of amplifier 13 is optional, depending on-the magnitude of thedifference voltage supplied by difie'rence circuit 14. The differencecircuit shown in FIG. 2 may be modified to eliminate diode 16 andresistor 19, connecting emitter of transistor 15 directly to thepositive output terminal. This results in slightly poorer regulation andnecessitates the Zener voltage of diode 17 being equal to the desiredoutput voltage. Other modifications to the circuitry shown will occur toa person skilled in the art and may be followed without departing fromthe sphere and scope of the invention as described in the claim below.

What is claimed is:

A transistor series voltage regulator for providing a regulated outputvoltage from an unregulated input voltage, comprising: a firsttransistor of the PNP type having its collector connected to a positiveoutput terminal; a negative terminal common to both input and output; afirst Zener diode connected in the reverse direction between a positiveinput terminal and the emitter of the first transistor; a first resistorconnected between the positive input terminal and the base of the firsttransistor; a second transistor of the NPN type; a second Zener diodeconnected in the reverse direction between the positive output terminaland the emitter of the second transistor; a second resistor connectedfrom the emitter of the second transistor to the negative terminal; athird Zener diode connected in the reverse direction from the base ofthe second transistor to the negative terminal, whereby the differencebetween the output voltage and the sum of the Zener voltages of thesecond and third Zener diodes is applied between the emitter and thebase of the second transistor; a third resistor connected from thepositive input terminal to the :base of the second transistor, forlimiting the current in the third Zener diode; a third transistor of thePNP type, having its collector connected to the positive outputterminal, its emitter connected to the base of the first transistor, andits base connected to the collector of the second transistor; and afourth resistor connected from the base of the third transistor to thepositive input terminal, whereby the base current of the thirdtransistor may reverse in response to large difference voltages. i

References Cited in the file of this patent UNITED STATES PATENTS2,693,568 Chase Nov. 2, 1952 2,751,549 Chase 'June 19, 1956 2,850,695Bishop Se t. 2, 1958 2,903,640 Bixby Sept. 8, 1959 OTHER REFERENCESDesign Considerations for Semiconductor Regulated Power Supplies, 'Sherrand Levy, Electronic Design, July 15, 1956, 'vol. 4, pages 22-25.

